U.S. Pat. No. 2,738,383 (Herr et al.) teaches that signals recorded on a master magnetic recording tape may be duplicated by placing face-to-face the magnetizable surfaces of the master tape and an unrecorded copy tape and moving them through a gradually diminishing field such as a magnetic idealizing field. By using a copy tape which has a relatively low Curie temperature and a master tape which has a higher Curie temperature, the copying can be carried out by heating the copy tape at least to its Curie temperature and then cooling it below its Curie temperature while in face-to-face contact with the master tape. U.S. Pat. No. 3,364,496 (Greiner et al.) accomplishes this using a copy tape which has a coating of ferromagnetic chromium dioxide particles having a Curie temperature of 120.degree.C. U.S. Pat. No. 3,465,105 (Kumada et al.) also concerns thermoremanent contact duplication and employs a copy tape having a coating of spherical magnetic powder. See also U.S. Pat. No. 3,632,898 (Slade et al.) which employs a copy tape having a layer of chromium dioxide particles.
Contact duplication has not been used commercially for making copies of audio tapes, in part because electronic equipment is available for making such copies at high speeds. As for video tapes, high speed electronic copying equipment is considered to be unfeasible so that efforts are being made to commercialize contact duplication techniques such as are described in the foregoing patents. However, the copying must be of high quality to compete with the exacting requirements established by the slower electronic copying.